Experimental Observation of Nonlinear Traveling Waves in Turbulent Pipe Flow

TLDR

Transition to turbulence in pipe flow, a longstanding fluid dynamics problem, is not predicted by linear stability theory yet profoundly impacts mass, momentum, and heat transport, and recent computational discoveries of unstable traveling waves have led to a proposed transition model. We experimentally observed these traveling waves in pipe flow, confirming the proposed transition scenario and indicating that the dynamics of these unstable states may underpin turbulent behavior.

Abstract

Transition to turbulence in pipe flow is one of the most fundamental and longest-standing problems in fluid dynamics. Stability theory suggests that the flow remains laminar for all flow rates, but in practice pipe flow becomes turbulent even at moderate speeds. This transition drastically affects the transport efficiency of mass, momentum, and heat. On the basis of the recent discovery of unstable traveling waves in computational studies of the Navier-Stokes equations and ideas from dynamical systems theory, a model for the transition process has been suggested. We report experimental observation of these traveling waves in pipe flow, confirming the proposed transition scenario and suggesting that the dynamics associated with these unstable states may indeed capture the nature of fluid turbulence.